SK287139B6 - Method for the preparation of citalopram - Google Patents

Abstract

A method for the preparation of citalopram comprising reaction of a compound of formula (IV), wherein R is C1-6 alkyl, acyl, C1-6 alkylsulfonyl or arylsulfonyl, with 3-(N,N-dimethylamino)-propyl magnesium halide.

Description

Technical field

The invention relates to a process for the preparation of the well-known antidepressant drug citalopram, 1- [3- (dimethylamino) propyl] -1- (4-fluorophenyl) -1,3-dihydro-5-isobenzofuran-carbonitrile.

BACKGROUND OF THE INVENTION

Citalopram is a well known antidepressant drug that has been on the market for several years and has the following structure:

Citalopram is a selective, centrally acting serotonin reuptake inhibitor (5-hydroxytryptamine; 5-HT) and therefore has antidepressant effects. The antidepressant activity of this compound has been described in several publications, for example in J. Hyttel, Prog. Neuro-Psychopharmacol. & Biol. Psychiatry. 6, 277-295 (1982) and A. Gravem, Acta Psychiatr. Scand. 75, 478-486 (1987). This compound is further described in EP-A 474 580 as a substance which is effective in the treatment of dementia and cerebrovascular disorders.

Citalopram was first disclosed in DE 2,657,271, which corresponds to U.S. Pat. No. 4,136,193. This patent discloses one method of preparing citalopram and suggests other methods that can be used to prepare citalopram.

According to the described process, the preparation is carried out by reacting the corresponding 1- (4-fluorophenyl) -1,3-dihydro-5-isobenzofuranocarbonitrile with S-N, N-dimethylaminobutyl chloride in the presence of methylsulfonylmethide as a condensing agent. The starting material was prepared from the corresponding 5-bromo derivative by treatment with cuprous cyanide.

According to only the generally indicated method, citalopram can be synthesized by ring closure by cyclization of a compound of formula (II)

(II) in the presence of a dehydrating agent followed by exchange of the 5-bromo group with cuprous cyanide. The starting material of formula (II) is prepared from 5-bromophthalide by two consecutive Grignard reactions, i.e. with 4-fluorophenyl-magnesium chloride or N, N-dimethylarmnopropylmagnesium chloride.

U.S. Pat. No. 4,650,884 discloses a novel and unexpected process for the preparation of citalopram according to which an intermediate of formula (III)

(III) undergoes a cyclization reaction by dehydration with strong sulfuric acid to give citalopram. The intermediate of formula (III) was prepared from 5-cyanophthalide by two consecutive Grignard reactions, i.e. reactions with 4-fluorophenyl magnesium halide and N, N -dimethylaminopropyl magnesium halide.

Other methods of preparation are described in International Patent Applications WO 98 019 511, WO 98 019 512 and WO 98 019 513. WO 98 019 512 and WO 98 019 513 relate to methods in which 5-amino-, 5-carboxy- or The 5- (sec-aminocarbonyl) phthalide is subjected to two consecutive Grignard reactions, ring closure and conversion of the resulting 1,3-dihydroisobenzofuran derivative to the corresponding 5-cyano compound, i.e. citalopram. International patent application WO98019511 describes a process for the preparation of citalopram in which a (4-substituted-2-hydroxymethylphenyl- (4-fluorophenyl) methanol compound was subjected to a cyclization reaction and the resulting 5-substituted 1- (4-fluorophenyl-1,3-dihydro) The isobenzofuran was converted to the corresponding 5-cyano derivative, which was alkylated with (3-dimethylamino) propyl halide to citalopram.

Methods for preparing the individual enantiomers of citalopram are described in U.S. Patent 4,943,590; it is clear from the description that the ring closure of the intermediate of formula (III) may be carried out via a volatile ester with a base.

It has now unexpectedly been found that citalopram can be produced in a novel, convenient and safe manner using conventional starting materials.

SUMMARY OF THE INVENTION

The present invention provides a process for the preparation of citalopram, wherein the compound of formula (IV) is

(IV), wherein R is _{R 6} C alkyl, acyl, C _{R 6} - alkylsulfonyl, treated with 3 - (, V, W-dimethylamino) propylmagnéziumhalogenidom, preferably of 3- (Λζ-dimethylamino) propylmagnesium chloride to obtain citalopram of formula (I)

which is isolated in the form of a base or in the form of a pharmaceutically acceptable salt thereof.

In another aspect, the invention includes a novel intermediate of formula (IV).

In another aspect, the invention relates to processes for preparing an intermediate of formula (IV).

In yet another aspect, the invention includes the use of compounds of formula (IV) for the preparation of a racemic compound of formula (III)

(III).

In yet another aspect, the invention relates to an antidepressant pharmaceutical composition comprising citalopram prepared by the method of the invention.

According to the invention, citalopram is obtained by a single step Grignard reaction from the compounds of formula (IV) wherein R is C _r C _(j - alkyl, acyl, C | - ₍₎ -alkylsulfonyl or arylsulfonyl

(IV).

The product of said Gringnard reaction unexpectedly spontaneously closes the ring (cyclizes) directly to citalopram and therefore reaction of the compound of formula (IV) with the Grignard reagent results in citalopram in one reaction step.

According to the invention, the compounds of formula (IV) can be prepared in three different ways.

One of these methods involves the protection of (4-cyano-2-hydroxymethylphenyl) (4-fluorophenyl) methanol hydroxymethyl alcohol of formula (VI)

R

I o

followed by oxidation to give a compound of formula (IV), wherein R is C _r C ₆ - alkyl, acyl, C, - ₆ - alkylsulfonyl or arylsulfonyl.

Said oxidation of the compounds of formula (V) may be carried out by any conventional oxidizing agent, preferably Na ₂ WO ₄ .

The starting material for the preparation of the compound of formula (VI) can be prepared as described in the international patent application PCT / DK97 / 00 511.

Another method for preparing compounds of formula (IV) involves reacting 5-cyanophthalide with 4-fluorophenyl magnesium halide, preferably 4-fluorophenyl magnesium bromide; followed by reaction with RX, wherein R is as defined above and C is a displaceable group, preferably X is pivaloyl chloride, 3,5-dimethoxybenzoyl chloride, methyl iodide, ethyl bromide, tosyl chloride, Me ₂ SO ₄ or MeSO ₂ Cl.

The reaction can be illustrated as follows:

The starting material is 5-cyanophthalide, which can be prepared as described in Tirouflet J., Bull. Soc. Sci. Bretagne 26, 35 (1959).

In a third process for preparing a compound of formula (IV), one of the enantiomers of a compound of formula (III), i.e., the R-enantiomer, is protected and dehydrated to give a compound of formula (VII) which is oxidized to a ketone of formula (IV) .

CN

In this way, the R-enantiomer of formula (III) can be used to prepare racemic citalopram.

The oxidative cleavage of the compound of formula (VII) is carried out by oxidation, preferably with MnO ₄ (permanganates) or ozone, RuCl ₃ , OsO ₄ .

Citalopram is marketed as an antidepressant drug in the form of a racemate; but in the near future, the effective S-enantiomer of citalopram will be marketed.

The active 6'-enantiomer of citalopram can be prepared from a compound of formula (III) by separating the 6'-enantiomer and the R-enantiomer and then cyclizing the S-enantiomer as described in U.S. Patent 4,943,590. departments have not yet been used.

According to another aspect of the invention, after the R-enantiomer of a compound of formula (III) has been converted to an optically inactive compound of formula (IV), a racemic compound of formula (III) can be prepared from this:

Said racemic compound of formula (III) may be resolved into optically active enantiomers as described in U.S. Patent 4,943,590, and the obtained S-enantiomer of the compound of formula (III) is used to prepare S-citalopram. The R-enantiomer of the compound of formula (III) can be recycled again in the described production cycle.

In this way, the R-enantiomer of formula (III) can be converted to 5-citalopram.

SK 287139-6

Other reaction conditions, solvents, and the like for the described reactions are common to this type of reactions and can be readily determined by one of skill in the art.

In this specification and claims the term C 1-6 alkyl is used to mean a straight or branched alkyl group having from one to six (inclusive) carbon atoms such as methyl, ethyl, 1-propyl, 2-propyl, 1-butyl, butyl, 2-methyl-2-propyl, 2,2-dimethyl-1-ethyl and 2-methyl-1-propyl.

The term aryl refers to a mono- or bicyclic carbon aromatic group, such as phenyl and naphthyl, especially phenyl, or ring substituted phenyl.

The term heteroaryl refers to a mono- or bicyclic heterocyclic aromatic group such as indolyl, thienyl, pyrimidyl, oxazolyl, isoxazolyl, thiazolyl, isothiazolyl, imidazolyl, benzofuranyl, benzothienyl, pyridyl and furanyl, especially pyrimidyl, indolyl and thienyl.

The term acyl is used herein to mean a C _1-6 alkylcarbonyl or arylcarbonyl or heteroarylcarbonyl group, wherein the C 1-6 -alkyl and the aryl and heteroaryl are as defined above.

Halogen means chlorine, bromine or iodine.

A preferred exchangeable group is a halide or sulfonate.

In a preferred embodiment of the invention, R is acyl, preferably pivaloyl, acetyl or optionally substituted benzoyl.

Said compound of formula (I) may be used in the form of the free base or in the form of a pharmaceutically acceptable acid addition salt. As acid addition salts, salts formed with organic or inorganic acids can be used. Examples of these acid addition salts include those formed with maleic, filmaric, benzoic, ascorbic, succinic, oxalic, bismethylenesalicylic, methanesulfonic, ethanedisulfonic, acetic, propionic, tartar, salicylic, citric, gluconic, lactic acid, lactic acid, lactic acid, malic acid, lactic acid, lactic acid. , aspartic, stearic, palmitic, itaconic, glycolic, p-aminobenzoic, glutamic, benzenesulphonic and theophylline acetic, as well as with 8-halo-theophylline, for example with 8-bromo-theophylline. Examples of inorganic addition salts are those with hydrochloric, hydrobromic, sulfuric, sulfamic, phosphoric and nitric acids.

Acid addition salts of the compounds may be prepared by methods known in the art. The base is reacted or with a calculated amount of acid in a water miscible solvent environment such as acetone or ethanol and then the salt is isolated by concentration and cooling, or the base is mixed with excess acid in a water immiscible solvent environment such as ethyl ether, ethyl acetate or ethanol. dichloromethane, the salt precipitating spontaneously.

The pharmaceutical compositions of the invention may be administered by any suitable means and in any suitable form, for example orally in the form of tablets, capsules, powders or syrups, or parenterally in the form of usual sterile injectable solutions.

The pharmaceutical compositions of this invention may be prepared by conventional methods known in the art. For example, tablets may be prepared by mixing the active ingredient with conventional carriers and / or diluents and subsequently compressing the mixture in conventional tabletting machines. Examples of carriers or diluents include corn starch, potato starch, talc, magnesium stearate, gelatin, lactose, gums and the like. Any other ingredients such as coloring, flavoring and preservative and the like may be used as long as they are compatible with the other ingredients.

Solutions for injections may be prepared by dissolving the active ingredient and acceptable ingredients in a portion of the solvent for injection, preferably sterile water, adjusting the solution to the required volume of the formulation, sterilizing the solution and filling it in suitable ampoules or vials. Any commonly used additive may be added, for example to adjust the osmotic pressure, preservation, antioxidants and the like.

The invention is illustrated by the following examples.

DETAILED DESCRIPTION OF THE INVENTION

Example 1

2,2-Dimethylpropionic acid 5-cyano-2- [1- (4-fluorophenyl) -1-hydroxymethyl] benzyl ester

To a solution of (4-cyano-2-hydroxymethylphenyl) (4-fluorophenyl) methanol (9.2 g, 0.037 mol) and triethylamine (4.0 g, 0.04 mol) was added pivaloyl chloride (4.2 g, 0.039 mol). The reaction mixture was stirred for 60 minutes and then poured onto ice, extracted with diethyl ether (2 x 75 mL), dried (anhydrous magnesium sulfate) and concentrated under reduced pressure to give a colorless oil (12.0 g). The residue was purified by chromatography (hexane / ethyl acetate 1: 9) to give the title compound (8.2 g, 70%).

@ 1 H NMR (DMSO-d6) _.delta . δ 1.1 (s, 9H); 5.15 (m. 2H); Δ (broad s, 1H); 6.25 (d, J = 6Hz, 1H); 7.1-7.2 (m, 2H); 7.3-7.4 (m, 2H); 7.7-7.9 (m, 3H).

Example 2

2,2-Dimethylpropionic acid 5-cyano-2- [1- (4-fluorophenyl) -methanoyl] benzyl ester

To a solution of 2,2-dimethylpropionic acid 5-cyano-2- [1- (4-fluorophenyl) -1-hydroxymethyl] benzyl ester (8.0 g, 0.025 mol) in ethyl acetate (20 mL) was added peroxide solution with stirring hydrogen (30% aqueous solution, 10 g, 0.079 mol), Na ₂ WO ₄ .2H ₂ O (0.15 g, 0.0005 mol) and (N-octyl) ₃ NCH ₃ .HSO ₄ (0, 23 g, 0.0005 mol). The mixture was then heated at reflux for 4 hours; then allowed to cool to room temperature and poured into dilute hydrochloric acid, extracted with diethyl ether (2 x 50 mL), dried (anhydrous magnesium sulfate) and concentrated under reduced pressure to give the title ketone compound (7.8 g, 97.5% of the theoretical yield).

Example 3

Acetic acid 5-cyano-2- [4-dimethylamino-1- (4-fluorophenyl) -but-1-enyl] benzyl ester and oxalic acid salt

Procedure 3A

To a solution of 4- [4-dimethylamino-1- (4-fluorophenyl) -1-hydroxybutyl] -3-hydroxymethylbenzonitrile (72 g, 0.21 mol) in acetonitrile (438 g) was added dropwise with stirring at 20 ° C acetic anhydride (103 g, 1 mol) was added. After the anhydride addition was complete, trimethylsilyl chloride (5.5 g, 0.05 mol) was added dropwise (exothermic reaction, temperature increased from 20 to 28 ° C) and the reaction mixture was stirred overnight. Concentrated sulfuric acid (14.5 g, 0.14 mol) was then added to the reaction mixture and the mixture was heated to 50 ° C for 30 minutes (HPLC showed complete reaction). After cooling the reaction mixture, the mixture was concentrated under reduced pressure and neutralized with aqueous ammonia (23%) and extracted with toluene (2 times). The organic phase was dried (MgSO ₄ ) and concentrated under reduced pressure to give the title compound as a light orange oil (69.5 g, 85%).

The product was characterized after conversion to oxalic acid salt. A warm solution of oxalic acid (1 g, 0.0177 mol) in methanol (50 mL) was added to a stirred solution of the title alkene compound (6.63 g, 0.0173 mol) in methanol (50 mL). The mixture was allowed to cool, the precipitated crystal was collected by filtration (7.4 g) and washed with cold methanol (10 mL). Mp 168 ° C. 1 H NMR (DMSO-d ₆ ): δ 1.9 (s, 3H); 2.2 (m. 2H); 2.62 (s, 6H); 3.1 (t, J = 6.2Hz, 2H); 4.8 (s. 2H); 6.35 (t, J = 7Hz, 1H); 7.1-7.25 (m, 4H); 7.42 (d, J = 7Hz, 1H); 7.9 to 8 (m, 2H).

¹³ C NMR (DMSO-d 6): δ 20.35 24.98, 42.16, 55.54, 62.51, 111.17, 115.25, 115.59, 118.51, 124.85, 128 , 0, 128.18, 131.32, 132.43, 132.73, 135.65, 135.99, 138.68, 142.9, 164.72, 169.96.

Analysis calculated for C ₂₄ H ₂₅ N ₂ O ₆ F: 63.14% C, 5.53% H, 6.14% N; found: 63.1% C, 5.58% H, 6.12% N.

Acetic acid 5-cyano-2- [4-dimethylamino-1- (4-fluorophenyl) -but-1-phenyl] benzyl ester

Procedure 3 B

To a solution of 4- [4-dimethylamino-1- (4-fluorophenyl) -1-hydroxy-butyl] -3-hydroxymethyl-benzonitrile (1000 g, 2.9 mol) in acetonitrile (1000 g) acetic anhydride (1112 g, 10.8 moles) was added dropwise with stirring at 20 ° C. The exothermic reaction raised the temperature of the reaction mixture from 20 to 50 ° C. Concentrated sulfuric acid (300 g, 3 moles) was then added to the reaction mixture, and the mixture was heated at 50 ° C for 3 hours (HPLC showed the reaction to be complete). After cooling, the reaction mixture was concentrated under reduced pressure and neutralized with aqueous ammonia (25%) and extracted with toluene (2 times). The organic phase was dried (MgSO ₄ ) and concentrated under reduced pressure to give the title compound as a light orange oil (1023 g, 92%).

Example 4

2,2-Dimethylpropionic acid 5-cyano-2- [4-dimethylamino-1- (4-fluorophenyl) but-1-enyl] benzyl ester and oxalic acid salt

Procedure 4A

To a solution of 4- [4-dimethylamino-1- (4-fluorophenyl) -1-hydroxy-butyl] -3-hydroxymethyl-benzonitrile (72 g, 0.21 mol) and triethylamine (25.0 g, 0.247 mol) In acetonitrile (438 g), a solution of pivaloyl chloride (26.0 g, 0.215 mol) was added dropwise with stirring at 20 ° C. After stirring for 60 minutes, concentrated sulfuric acid (40 mL) was added dropwise to the reaction mixture, and the mixture was heated to 70 ° C for 180 minutes. After cooling, the reaction mixture was neutralized with aqueous ammonia solution (25%) and extracted with diethyl ether. The organic phase was dried (MgSO ₄ ) and concentrated under reduced pressure to give the title compound as a yellow oil (82 g, 96%).

The product was characterized after conversion to oxalic acid salt (acetone). Mp 188 ° C.

1 H NMR (DMSO-d 6): δ 1.07 (s, 9H); 2.2 (m. 2H); 2.6 (s. 6H); 3.05 (t, J = 6.2Hz, 2H); 4.725 (d, J = 12Hz, 1H); 4.85 (d, J = 12Hz, 1H); 6.3 (t, J = 6.3Hz, 1H); 7.1-7.3 (m, 4H); 7.42 (d, J = 7Hz, 1H); 7.9 to 8 (m, 2H).

¹³ C NMR (DMSO-d ₆ ): δ 25.1 26.71, 42.3, 55.67, 62.55, 111.21, 115.3, 115.64, 128.17, 131.33, 132.28, 136.13, 138.58, 142.76 164.4.

Analysis calculated for C 27 composition _3] N ₂ O ₆ F: 65.04% C, 6.28% H, 5.62% N; H, 6.63; N, 5.60.

2,2-Dimethylpropionic acid 5-cyano-2- [4-dimethylamino-1- (4-fluorophenyl) but-1-enyl] benzyl ester and hydrochloric acid salt

Procedure 4B

To a solution of 4- [4-dimethylamino-1- (4-fluorophenyl) -1-hydroxy-butyl] -3-hydroxymethyl-benzonitrile (85.5 g, 0.21 mol) in acetonitrile (290 mL) was added. pivaloyl chloride solution (30.1 g, 0.25 mol) was added dropwise with stirring at 0 ° C. After stirring for 60 minutes, concentrated sulfuric acid (32.5 g, 0.33 mol) was added dropwise to the reaction mixture and heated to 70 ° C for 180 minutes after the acid addition was complete. After cooling to room temperature, acetonitrile (220 mL) was removed under reduced pressure and the reaction mixture was neutralized with aqueous ammonia (23%) and extracted with diethyl ether. The organic phase was dried (MgSO ₄ ) and concentrated under reduced pressure to give the title compound as a pink oil (102.1 g).

A solution of the title alkene (II) (50.0 g, 0.11 mol) in methanol was added to an anhydrous solution of HCl in methanol (200 mL) with stirring. After stirring at room temperature for 30 minutes, the solvent was removed under reduced pressure. Diethyl ether was added and the white precipitate was collected by filtration, washed with diethyl ether to give the title hydrochloride (48.1 g). The product had a melting point of 165 ° C.

2,2-Dimethylpropionic acid 5-cyano-2- [4-dimethylamino-1- (4-fluorophenyl) but-1-enyl] benzyl ester, hydrogen sulphate

Procedure 4C

To a solution of 4- [4-dimethylamino-1- (4-fluorophenyl) -1-hydroxy-butyl] -3-hydroxymethyl-benzonitrile (85.5 g, 0.21 mol) in acetonitrile (290 mL) was added. pivaloyl chloride solution (29 g, 0.24 mol) was added dropwise with stirring at 0 ° C. After stirring for 60 minutes, concentrated sulfuric acid (32.5 g, 0.33 mol) was added dropwise to the reaction mixture and heated to 70 ° C for 180 minutes after the acid addition was complete. After cooling to room temperature, acetonitrile was removed under reduced pressure, toluene (200 ml) was added and again removed under reduced pressure to give the title compound as a pink oil (HM g).

2,2-Dimethylpropionic acid 5-cyano-2- [4-dimethylamino-1- (4-fluorophenyl) but-1-phenyl] benzyl ester hydrochloride

Procedure 4D

To a solution of 4- [4-dimethylamino-1- (4-fluorophenyl) -1-hydroxybutyl] -3-hydroxymethylbenzonitrile (21.35 g, 0.052 mol) in acetonitrile (21.35 g) was added. pivaloyl chloride solution (7.6 g, 0.063 mol) was added dropwise with stirring at room temperature. Upon completion of the addition, a solution of methanesulfonyl chloride (6.1 g, 0.053 mol) in CH ₂ Cl ₂ (50 mL) was added, followed by triethylamine (10.6 g, 0.105 mol). The mixture was further stirred for 30 minutes, poured into water, extracted with CH ₂ C1 _2, the organic phase was dried _(MgSO4) and concentrated in vacuo. The resulting oil was then dissolved in anhydrous ethanol / HCl, concentrated under reduced pressure, treated with diethyl ether, and filtered to give the said alkene salt as the hydrochloride (22.6 g, 98%).

Example 5

2,2-Dimethylpropionic acid 5-cyano-2- [1- (4-fluorophenyl) -methanoyl] -benzyl ester

Procedure 5A

To a solution of the alkene of 5-cyano-2- [4-dimethylamino-l- (4-fluoro-phenyl) -but-l-enyl] -benzyl ester 2,2-dimethyl (165 g, 0.337 mol) in _H2O (1 100 mL) was added a solution of sodium permanganate in water (40%) (3.7 mol) at such a rate that the reaction temperature was maintained between 45 and 50 ° C.

After the addition was complete, the reaction mixture was allowed to cool to room temperature and filtered. The filter solid was washed with cold water (3 x 150 mL), stirred in acetone (2000 mL), filtered off; evaporation gave the crude ketone, which was purified by filtration through a silica column (eluent hexane: ethyl acetate 8: 2). In this way the title ketone was obtained as a pure compound (82 g, 75%), m.p. 81 ° C.

1 H NMR (DMSO-d ₆ ): δ 0.9 (s, 9H); 5.1 (s. 2H); 7.35 to 7.5 (m, 3H); 7.65 (d, J = 7Hz, 1H); 7.8 to 7.9 (m, 2H); 8.0 (m, IH); 8.1 (s, 1 H).

¹³ C NMR (DMSO-d 6: δ 26.5, 63.01, 113.183, 116.0, 116.36, 118.02, 129.35, 132.19, 132.58, 133.03, 133.018, 133 , 34, 135.98, 141.7, 163.62, 167.65, 176.87, 193.94.

Analysis calculated for C ₂₀ H ₁₈ NO ₃ F: C 70.79, H 5.35, N 4.13; Found: C, 70.49; H, 5.30; N, 4.07.

2,2-Dimethylpropionic acid 5-cyano-2- [1- (4-fluorophenyl) -methanoyl] -benzyl ester

Procedure 5B

Solution of 5-cyano-2- [4-dimethylamino-l- (4-fluoro-phenyl) -but-enylj-benzyl ester 2,2-dimethyl ester (38.0 g, 0.093 mol) in _H2O (1 300 mL) and HCl (70 mL) were monitored by HPLC. A white precipitate formed during the reaction. After completion of the reaction, the white solid was collected by filtration, washed with water and dried under reduced pressure to give the title ketone as a pure compound (22.5 g, 72%).

2,2-Dimethylpropionic acid 5-cyano-2- [1- (4-fluorophenyl) -methanoyl] -benzyl ester

Procedure 5C

To a solution of the suspension of 5-cyano-2- [4-dimethylamino-1- (4-fluorophenyl) -but-1-enyl] -benzyl 2,2-dimethylpropionate, H ₂ SO ₄ (11.0 g, 0.022 mol) ) in water (250 mL) and ethyl acetate (100 mL) were added sodium periodate (30 g, 0.14 mol) and RuCl ₃ hydrate (0.35 g). The suspension was stirred vigorously at room temperature for 16 hours. The suspension was then filtered through a pad of silica. The organic phase was separated and washed with water (50 mL). Evaporation of the solvent in vacuo gave the title compound as an oil which crystallized on standing. Yield: 7.4 g (99% of theory).

Example 6

2,2-Dimethylpropionic acid 5-cyano-2- [1- (4-fluorophenyl) -methanoyl] -benzyl ester

A solution of 4-fluorophenylmagnesium bromide, prepared from 4-fluorobromobenzene (19.2 g, 0.11 mol) and magnesium chips (3.2 g, 0.13 mol) in dry THF (100 mL) was added dropwise to a suspension of 5- cyanophthalide (15.9 g, 0.1 mol) in dry THF (150 mL). The temperature of the reaction mixture was kept below 5 ° C. After the addition was complete, the reaction mixture was stirred overnight at room temperature.

Pivaloyl chloride (13.3 g, 0.11 mol) was added to the reaction mixture and the temperature was maintained at 60 ° C for 2 hours. The resulting solution was added to a saturated solution of ammonium chloride (100 mL, aqueous) with ice (50 g). Diethyl ether was then added and after phase separation, the organic phase was washed with aqueous sodium hydroxide solution ((c 4 _and 0 H = 0.1 mol.dm ³ ) (2 x 100 mL) and water (100 mL), dried over MgSO ₄ . Evaporation of the solvents afforded the title compound in the crude state (29.8 g, 88%) as an oil, which was considered pure enough to be used in the next reaction.

The pure form was obtained by crystallization from ethyl acetate and n-heptane (1: 9). The title compound was obtained as off-white crystals.

Example 7 1- (3-Dimethylamino-propyl) -1- (4-fluorophenyl) -1,3-dihydro-isobenzofuran-5-carbonitrile and its oxalic acid salt

To a solution of 2,2-dimethylpropionic acid 5-cyano-2- [1- (4-fluorophenyl) -methanoyl] -benzyl ester (28.5 g, 0.084 mol) in anhydrous THF (150 mL) at 0 ° C was added a solution 3 (the ^{r-Dimethylamino)} propyl magnesium chloride (2.2 equivalents) and the reaction followed by HPLC. After stirring at 0 ° C for one hour, saturated ammonium chloride solution was added and the mixture was extracted with ethyl acetate, dried (anhydrous sodium sulfate) and concentrated under reduced pressure to give the title compound as an oil (28.0 g of 87%). % by HPLC). The oxalic acid salt was obtained by crystallization from acetone.

Example 8

4- [l- (4-Fluoro-phenyl) -methanoyl] -3-hydroxymethyl-benzonitrile

5-Cyano-2- [1- (4-fluorophenyl) -methanoyl] -benzyl 2,2-dimethylpropionate (20 g, 0.061 mol) was added to freshly prepared sodium methanolate (sodium 0.25 g, in 100 mL) methanol) and at room temperature, the reaction mixture was stirred until HPLC control showed complete deprotection. The methanol was then removed under reduced pressure, the residue was dissolved in MTBE, washed with saturated ammonium chloride solution and dried (MgSO ₄ ); concentration under reduced pressure gave the title ketone without protecting group (14.6 g).

Example 9

4- [4-Dimethylamino-l- (4-fluoro-phenyl) -l-hydroxy-butyl] -3-hydroxymethyl-benzonitrile

To a solution of 4- [1- (4-fluoro-phenyl) -methanoyl] -3-hydroxymethyl-benzonitrile ketone (15.0 g, 0.046 mol) in anhydrous THE at 0 ° C was added a solution of 3 - (V, A). (dimethylamino) propylmagnesium chloride (2.2 equivalents) and the progress of the reaction was monitored by HPLC. After an hour at 0 ° C, saturated ammonium chloride solution was added and the mixture was extracted with MTBE, dried (MgSO ₄ ) and concentrated under reduced pressure to give the title compound as an oily substance (16.7 g, 85% purity). .

Claims (10)

PATENT CLAIMS A process for the preparation of citalopram, characterized in that the compound of formula (IV) wherein R is acyl is treated with 3- (N, N-dimethylaminopropyl) magnesium halide to form citalopram of formula (IV). I) which is isolated as a base or as a pharmaceutically acceptable salt thereof. Process according to claim 1, characterized in that the intermediate of formula (IV) is prepared by oxidation of the corresponding compound of formula (V) (V) in which R is as defined in claim 1. A process according to claim 2, characterized in that the compound of formula (V) is prepared by protecting (4-fluorophenyl) (4-cyano-2-hydroxymethylphenyl) (4-cyano-2-hydroxymethylphenyl) methanol. Process according to claim 1, characterized in that the intermediate of formula (IV) is prepared by oxidative cleavage of the corresponding compound of formula (VII) (VII), wherein R is as defined in claim 1. Method according to claim 4, characterized in that the oxidative cleavage of the compound of the general formula (VII) is carried out by oxidation, preferably with MnO 2 (permanganates) or ozone, RuCl ₃ , OsO ₄ . Process according to any one of claims 4 to 5, characterized in that the alkene intermediate of formula (VII) is prepared by protecting and dehydrating the corresponding compound of formula (III) (III), wherein the compound of formula (111) is the en-enantiomer. A process according to claim 1, characterized in that the intermediate of formula (IV) is prepared by reacting 5-cyanophthalide with 4-fluorophenyl magnesium halide followed by RX to prepare a ketone of formula (IV), wherein R is determined by in claim 1 and X is a removable group. The process according to claim 1, wherein the compound of formula (IV) is reacted with 3- (N, N-dimethylamino) propyl magnesium chloride. Process according to claim 1, characterized in that the compound of formula (IV) is prepared by reacting 5-cyanophthalide with 4-fluorophenyl magnesium bromide. A process according to any one of claims 1 to 9, wherein R is pivaloyl, acetyl or optionally substituted benzoyl.